Previous studies on the neural mechanism of color vision have made progresses at multiple levels. At the neuronal level, an emerging view is that color information is coded in primary visual area (V1) by two classes of neurons: single-opponent neurons that receive balanced inputs from opposing cones, and double-opponent neurons that receive unbalanced cone inputs. But their relative roles in coding color information are still under debate. At the population level, spatially organized representation of color by groups of neurons have been found at many stages along the ventral visual pathway, including an area in human brain where lesions were associated with achromatopsia. The PI and colleagues have discovered such representations, or the hue maps, in areas V1 and V2 of macaque. The hue maps in different areas are likely to play a critical role in representing and processing color information. Anatomical and functional evidences suggest that the hue maps in V1 are likely the origin of the hue maps in other areas. But it is unknown how the hue maps in V1 are formed and how they differ from surrounding regions in the role of processing color information. The current project will address these questions by combining functional imaging with recording of many single units using multi- electrode arrays. The project aims to integrate and advance the knowledge at neuronal and population levels about the neural processing of color information. Such integration will bring together all the pieces that are needed to solve the puzzle of how color perception is produced. The trichromatic vision is only present in some primates among mammals. By studying the functional organization of color selective cells in macaque, the proposed project will shed light on how cortical circuits adapt to a change in peripheral during evolution. Such insights will be useful for understanding the origin of neural circuits involved in other functions, because many functions are products of adaptation to peripheral changes. Therefore, the impact of the proposed project is not limited to color vision.